Interpretive Summary: Biochar has received worldwide interests as a tool to solve various modern farming problems related to low-carbon soils. Holistic approach is necessary to achieve long-term benefits from long-lived biochar soil amendment. This study utilized first principles in soil chemistry and pollutant binding phenomena to tailor biochars for a specific purpose: heavy metal sequestration, carbon capture and strage, and/or crop yield enhancement. Results from this study can help build recommendations for “best management practice” for case-by-case biochar utilization in agricultural and non-agricultural soils.

Technical Abstract:
Heavy metals and agrochemicals are the key targets for biochar-induced mitigation of runoff/groundwater contamination. Inorganic and organic contaminants interact differently with biochars as well as soil components. Mechanistic understandings are needed on sorption, desorption, and competitive sorption of inorganic and organic contaminants together and separately. This study utilized (1) attenuation of pyrolysis parameters, (2) in situ and ex situ characterization of bulk and soluble (e.g., DOC fractions by fluorescence EEM/PARAFAC analyses) carbon components, and (3) batch sorption-desorption experiments, along with equilibrium speciation calculations. For heavy metals (Pb, Cu, Ni, Cd), surface-bound (e.g., carboxyl) and soluble organic ligands, and inorganic (especially P) components of biochar were the primary controlling parameters in both contaminated and agricultural soils. For triazine and organophosphorus agrochemicals, in contrast, specific surface area of biochar determined the extent of sorption. Depending on the properties of soil and biochar, complex competitive sorption behaviors were observed between organic and inorganic contaminants. In vitro gastrointestinal bioaccessibility testing results indicated that the biochar’s impact on Pb (and other heavy metals) mobility does not always translate into the impact on bioavailability.